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Chapter 25: Plant Nutrition and Transportation

by: Juliet Villegas

Chapter 25: Plant Nutrition and Transportation AS.020.152

Marketplace > Johns Hopkins University > Biology > AS.020.152 > Chapter 25 Plant Nutrition and Transportation
Juliet Villegas

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Chapter 25 for General Biology II. Plant nutrition and transportation.
General Biology II
Rebecca Pearlman
Class Notes
General Biology II, Chapter 25, Plant Nutrition and transportation, plant nutrition, plant transportation
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This 4 page Class Notes was uploaded by Juliet Villegas on Sunday February 28, 2016. The Class Notes belongs to AS.020.152 at Johns Hopkins University taught by Rebecca Pearlman in Spring 2016. Since its upload, it has received 17 views. For similar materials see General Biology II in Biology at Johns Hopkins University.


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Date Created: 02/28/16
Chapter 25: Plant Nutrition and Transportation * Plant nutrition and transport: key concepts o Plants Acquire Mineral Nutrients from the Soil o Soil Organisms Contribute to Plant Nutrition o Water and Inorganic Solutes Are Transported in the Xylem o Organic Solutes Are Transported in the Phloem * Plants acquire mineral nutrients from the soil o Essential elements—their absence severely disrupts plant growth and reproduction. o Macronutrients—at least 1 g/kg of the plant’s dry matte o Micronutrients—less than 0.1 g/kg of the plant’s dry matter o The essential elements were identified by growing plants hydroponically—with roots in nutrient solutions instead of soil. o The six macronutrients were identified by growing plants hydroponically. Source Nutrients o Air o CO2 o Bacteria (in soil or roots) o Nitrogen o Soil o Water, hydrogen, and Os from water, minerals (esp. N, P, K) * Plant nutrition o Characteristic symptoms can be used to diagnose deficiencies of essential elements, and they can be provided by fertilizer. In Nature, soils are usually somewhat deficient in N * Soils o Soils provide: * Anchorage for mechanical support * Mineral nutrients and water from the soil solution * O2 for root respiration from air spaces between soil particles * Beneficial soil organisms: bacteria, fungi, protists, earthworms, arthropods * The complexity of soil (don’t forget fungi!) * Soil organisms contribute to plant nutrition o One gram of soil contains 6,000 to 50,000 bacterial species and up to 200 meters of fungal hyphae! o Many consume dead and living plant material. o Many plants have symbiotic relationships with bacteria and fungi: o Mycorrhizal fungi o Nitrogen-fixing rhizobia bacteria o soil is an ecosystem (this is why it is difficult to restore soil) o Formation of mycorrhizae: * Roots produce signal molecules that stimulate growth of fungal hyphae toward the root. * The fungi produce signals that stimulate expression of plant symbiosis-related genes. * Fungal hyphae grow into roots and form structures where nutrients are exchanged. * Roots send signals for colonization Plant roots send chemical signals to arbuscular mycorrhizal fungi (A) and nitrogen-fixing bacteria (B) to stimulate colonization. Both processes do not occur in all plants. * Ion exchange o Root hair cells actively pump protons (H+) out of the cells * Clay has more affinity for H+ than cations, so protons change places with the cations * Goal: free cations from the clay so root hairs can take them up * Crop harvesting and leaching can deplete soil nutrients. Three ways to replenish: o 1. Shifting agriculture: crop rotation o 2. Organic fertilizers: humus, manure o 3. Chemical fertilizers: o Characterized by their “N-P-K” percentages o Produced in manufacturing processes that require a lot of energy. o Fungal plant partners * Mycorrhizal fungi * Root hairs better able to absorb water and minerals (especially Phosphorus * Expand root surface area up to 1000-fold o Bacterial plant partners * Nitrogen-fixing bacteria * Convert nitrogen (N2) from air into ammonia (NH3) o Benefit of crop rotation * Legumes enrich the soil for other plants because of their bacterial plant partners o Carnivorous plants obtain some nutrients (especially nitrogen) by digesting arthropods. * Trap has food for fly * Fly touches hair inside trap à no effect * Fly touches a 2nd hair within 20 sec * Trap snaps shut * Plant secretes enzymes to digest fly * Soil organisms contribute to plant nutrition o Plants cannot use atmospheric N2. o But some bacteria have nitrogenase to reduce N2 to NH3 (nitrogen fixation). o Fixation is a oxidation-reduction reaction and requires lots of energy. o Free-living rhizobia bacteria cannot reduce N2, but can infect plant (esp. legumes) roots and assume a form that does. * Soil organisms contribute to plant nutrition o Carnivorous plants obtain some nutrients by digesting arthropods. o The plants live in boggy, nutrient-poor soils. Digestion of arthropods provides nitrogen and phosphorus to the plant. * Why do plans need water? (Hint: what does the vacuole do?) o Answers: o Plants require water to carry out photosynthesis, to transport solutes between organs, to cool their bodies by evaporation, and to maintain internal pressure that supports their bodies. o Vacuole is filled with water and pushes against cell wall to provide turgor pressure (positive pressure that allows plant not to droop) * Water and solutes are transported in the xylem o Root cells take up water by osmosis. o FORGET: “WATER POTENTIAL ” AND “SOLUTE POTENTIAL ”!!! These terms are confusing. Just remember this: o In osmosis, the movement of water across membranes, water moves from a region of low solute concentration to one of higher solute concentration. Root cells have a higher solute concentration than that of the soil solution and water flows into the root. o Plant cells have tough walls and the pushing of the plasma membrane and the vacuole against the cell wall as water is taken up creates pressure that resists the further uptake of water. * Water and solutes are transported in the xylem o How does xylem move water to the tops of trees? o Transpiration—evaporation of water from cells in the leaves; forms water vapor o Cohesion of water molecules in the xylem sap due to hydrogen bonding o Tension (negative pressure) on the xylem sap resulting from transpiration o Transpiration also cools the leaves. o Evaporation of water from mesophyll cells consumes heat, decreasing the leaf temperature. o What drives transpiration? Why is heat consumed? o A large oak tree can transpire 40,000 gallons of water (151,000 liters) in a single growing season! o Stomata, or pores on leaves, regulate gas exchange and water loss— they can open or close by the action of the guard cells. o During day (in most plants), stomata open to allow CO2 to enter. o At night, stomata close to conserve water (may also close in daytime if water loss is too great). o Opening of stomata triggered by blue light. o Closing of stomata by a hormone and darkness. o Guard cells respond quickly to blue light. o Light absorbed by guard cell pigments activates a proton pump. H+ is actively transported out of cells. o Resulting electrochemical gradient drives K+ and Cl– into the guard cells, increasing solute concentration, and water enters by osmosis. o Increased turgor pressure in cells stretches them and open the stomata. o If pressure potential drops, the plant wilts. o Water will enter plant cells by osmosis until pressure potential balances solute potential. * Somata regulate gas exchange and transpiration * the guard cells are like an innertbue you might use in the swimming pool that you fill with air * difference btwn innertube and guard cells: air instead of water * Solutes are transported in the phloem by translocation o Translocation: movement of solutes through plant in the phloem, from sources to sinks. o Source: organ that produces or stores photosynthetic products (mostly sucrose)—leaves, storage roots, etc. o Sink: consumes sucrose for growth and storage—roots, flowers, fruit. o At a source, sucrose is actively transported into companion cells and into sieve tube elements. o Water enters sieve tube elements from xylem by osmosis because of the high [sucrose]. o This increases turgor pressure which pushes sieve tube contents towards the sink. o At the sink, sucrose moves out and water moves back to the xylem. o The gradient of solute potential and pressure potential needed for movement of phloem sap (translocation) is maintained. o Phloem transports solutes btwn sources and sinks o Source: organ that produces or stores sugars. o Sink: consumes sugars for growth and storage * Differences in water potential produce a pressure gradient that moves phloem sap from sources to sinks. * Xylem and phloem sap composition (mostly amino acids, sucrose respectively)


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